Really early Model 1803 rifles show up rarely, and I bought one yesterday. These early rifles differ considerably from the 1814-1820 production, and so I took some comparative pictures. First, of-course, is barrel length. The 1804 barrel is 31.125" long, the 1815 dated short rifle has a 33" barrel, and the 1814 dated long rifle has a .36" barrel. The stocks are correspondingly scaled in.length.
On the 1804 rifle, the buttplate toe is squared off, much like a civilian rifle of the period, and there is a flat under the buttstock from buttplate to trigger. On later production pieces the toe of the butt and the bottom of the stock is heavier and rounded.
The barrel wedge is different on all three rifles, with the 1804 key being quite flat and filed in the shape of a heart.
And of-course the box of the early piece is shorter and wider than the later versions.
Lots of other little things. If anyone needs photos
or measurements for a project, let me know. Incidentally, the bores vary a lot in these. The 1804 piece has a .538" bore with.a 42" twist. By contrast, the 1815 short rifle has a .525" bore and a 46" twist.